It is known from Philips Telecommunication Review, Vol. 41, No. 1, April 1983 “FM-900 series of VHF/UHF mobile radio telephone equipment” by F. P. van Enk, pages 36 to 45 to provide mobile radio units with microprocessors and a central control PROM (programmable read only memory) whereby personality data associated with a channel number can be stored. As a consequence, when a user selects a channel, the mobile radio unit adapts 1 itself in accordance with the stored data so that it is ready to operate without any further intervention by the user. Such a radio unit requires the PROM to be programmed using an external programmer.
It is also known to supply data, such as receiver identity codes, to digital pagers by over-the-air transmissions.
In the field of telecommunications, particularly digital paging, in order to enable a user to roam in different geographical areas which operate different systems and/or different characteristics it was necessary for a traveller to carry two or more portable units, each of the portable units being configured to operate in a respective area. One proposal for avoiding the need to carry several portable units is disclosed in European Patent EP-B-0 538 933. The portable unit is able to be reconfigured in response to data downloaded from a device, for example a plastics card carrying the data, inserted in an aperture or slot and read by the portable unit.
In view of the plethora of communications standards in force and coming into force it is desirable for equipment at each end of a link to be compatible.